物理 2002 年 DSE、CE 選擇題（第 3 頁）

21.

Which of the following is/are the reason(s) for **not** over-using ultra-violet lamps to produce a suntan effect ?

(1)Ultra-violet radiation is highly penetrating and will damage body tissue.

(2)Ultra-violet radiation has a strong heating effect and will damage body tissue.

(3)Over exposure to ultra-violet radiation may cause skin cancer.

22.

The figure shows the image of a foetus (a baby not yet born) taken by a scanner. Which of the following waves should be used in the scanning process ?

23.

CRO displays of Note X (complex waveform) and Note Y (sinusoidal waveform)

The above figures show the CRO displays of two musical notes $X$ and $Y$ . The settings of the CRO for the two notes are identical. Which of the following statements are correct ?

(1)Notes

X

and

Y

are of different qualities.

(2)Note

X

is of a higher pitch than note

Y

.

(3)Note

X

is louder than note

Y

.

24.

In the circuit shown, both ammeters $A_1$ and $A_2$ read $1$ A when the switch $S$ is open. Find the readings of the two ammeters when $S$ is closed.

Battery, 3 ohm resistor with ammeter A1, and 6 ohm resistor with switch S in parallel, with ammeter A2 in the main line

	$A_1$	$A_2$
	$0.5$ A	$1.5$ A
	$0.67$ A	$1$ A
	$1$ A	$1.5$ A
	$1$ A	$3$ A

25.

A stream of water from a tap attracted towards a plastic ruler

A plastic ruler is placed close to a stream of running water coming from an insulated tap. The stream of water is attracted towards the ruler as shown above. Which of the following statements are correct ?

(1)The ruler carries an electric charge.

(2)The ruler and the running water are attracting each other with forces of equal magnitude.

(3)Both positive and negative charges are induced on the running water

26.

Three parallel wires P, Q and R carrying equal currents out of the paper, R equidistant from P and Q

$P$ , $Q$ and $R$ are three parallel straight wires carrying equal currents flowing out of the paper. $R$ is equidistant from $P$ and $Q$ . What is the direction of the resultant force acting on $R$ by $P$ and $Q$ ?

Options A to D: arrow to the right, arrow to the left, arrow upwards, arrow downwards

27.

V against I graph with two straight lines X and Y from the origin, Y steeper; regions P (above Y) and Q (below X)

The figure above shows the voltage-current ( $V$ - $I$ ) graphs of two resistors $X$ and $Y$ . Which of the following deductions is/are correct ?

(1)The resistance of

X

is higher than that of

Y

.

(2)If

X

and

Y

are connected in series, the

V

-

I

graph of the combined resistor will lie in region

P

.

(3)If

X

and

Y

are connected in parallel, the

V

-

I

graph of the combined resistor will lie in region

Q

.

28.

Three identical lamps $L_1$ , $L_2$ and $L_3$ of ratings ' $6$ V, $12$ W' are connected to a $6$ V battery as shown in the figure. Which of the following statements is correct ?

Circuit with a 6 V battery, lamps L1 and L2 in parallel, in series with lamp L3

29.

Photograph of the inside of a plug with the live and neutral wires interchanged

If the live and neutral wires of an electric kettle are mistakenly interchanged inside the plug as shown above, which of the following will happen ?

30.

A radioactive isotope ${}^{234}_{90}\mathrm{Th}$ undergoes a series of decay processes to form a daughter ${}^{206}_{82}\mathrm{Pb}$ . How many $\alpha$ -particles and $\beta$ -particles have been emitted in this decay process ?

	No. of $\alpha$ -particles	No. of $\beta$ -particles
	$6$	$7$
	$7$	$6$
	$7$	$8$
	$8$	$7$